The present invention relates to a method of improving the ability to filter a clay slurry.
Clay materials are earth materials composed mainly of hydrated aluminum silicates. Various types of clay exist such as kaolinite, montmorillonite, attapulgite, bentonite, illite and ball clay.
Kaolinite or kaolin clay, for example, is a large volume raw material that is used in a number of applications. The largest single use of the material is in the production of glazed paper stocks. The incorporation of the clay into the paper results in a superior product which is used primarily for book and magazine production. A minor application for kaolin is as a raw material in certain ceramic systems. Other minor applications also exist.
Clays occur in scattered deposits worldwide. This naturally occurring material is mined, then undergoes further processing before use. In a typical kaolin mining operation, for example, the kaolin seam is uncovered by removing any overburden by mechanical means. Then the clay itself is removed, often by use of high pressure water streams directed against the clay deposit. Thus, a dilute suspension of the unrefined clay is collected and treated in order to yield the clay of commerce. Treatment of the raw clay is known as beneficiation. In a typical process, the raw kaolin slurry (about 25 percent solids) is treated with sulfuric acid and alum in order to flocculate the clay particles. The flocculated clay suspension is dewatered by filtering using rotary vacuum filters. The filter cake must then be re-suspended in water using polyacrylate dispersants and soda ash to yield a high solids slurry (60-70 percent solids), which is then sold. Alternately, the filter cake is dried and air floated to yield a fine dry powder which is also sold.
Currently, the bottleneck in the processes for obtaining clay is the filtration operation. This operation is both costly and time-consuming, but is necessary in order to produce a clay that possesses stable viscosity and color properties. Kaolin clays without these key properties are unacceptable in most applications. In order to increase productivity and lower costs to the producer, methods to facilitate this filtration are needed. Techniques for increasing throughput or lowering energy consumption during the filtering step would result in significant benefits for kaolin producers.
Other problems exist in the current beneficiation process. For example, the acids used during flocculation ultimately result in clays of commerce containing residual acids. The paper treated with acidic kaolin clay deteriorates more rapidly than paper treated with a non-acidic clay. Therefore, a preferred clay for use in paper treatment would be non-acidic.